Spathidexia sp. (French Guiana)
This specimen keys quite easily to Polygaster – it has the anterior katepisternal bristle ventral to the pleural suture and it has the trapezoidal scutellum with crossed apical bristles enclosed within crossed subapicals/laterals. But it differs from the description in Monty’s key by having a bare r1 and cu vein and hairs only on r4+5.
EDIT (26/11/2010): Monty has spotted that it looks more like the sister genus Spathidexia – the scutellars are slightly different and the hairs on the wing veins fit my example better.